Currently, in order to increase a communication bandwidth and achieve a higher user data throughput, a carrier aggregation (CA) technology is used in a Long-Term Evolution-Advanced (LTE-A) technology. A principle of the CA technology is that user communication data is carried on multiple carriers for communication. However, the introduction of the CA technology causes a great impact to an existing radio frequency receiver solution.
In the 3GPP (the 3rd-Generation Partnership Project) protocol R10 (Release 10), as shown in FIG. 1, the following three CA application scenarios are defined:
intra-band, continuous CA;
intra-band, non-continuous CA; and
inter-band, non-continuous CA, or also called inter-band CA, where
A and B represent two aggregated carriers.
For the intra-band continuous CA application scenario, a radio frequency receiver solution may still be implemented by using a single frequency synthesizer as in a conventional way; for the two complicated application scenarios: intra-band non-continuous CA and inter-band non-continuous CA, using multiple frequency synthesizers is an only option for the radio frequency receiver solution. However, mutual interference exists between the multiple frequency synthesizers, including mutual pulling (VCO Pulling) between voltage controlled oscillators (VCO) and spurious coupling and crosstalk of the VCOs, which is a major problem that hinders single-chip integration of multiple frequency synthesizers. It should be noted that: 1. mutual pulling between VCOs is a common mutual-interference phenomenon when multiple VCOs work simultaneously. Using a scenario in which two VCOs work simultaneously as an example, oscillation energy of VCO 1 is coupled to VCO 2, so that an output signal of VCO 2 includes a frequency component of oscillation frequency of VCO 1, thereby affecting receiving quality when VCO 2 is used as a receiving channel of a local oscillator signal. 2. spurious coupling and crosstalk of VCOs refers to various spurious components (unwanted frequency components), except desired frequency components, inevitably included in frequency components actually output by the VCOs. The spurious components may be generated for many reasons, and may be caused by a reference clock or may be caused by nonlinearity of a frequency synthesizer. In an application scenario with multiple frequency synthesizers and multiple receiving channels, if a spurious component output by one of the VCOs is coupled to another receiving channel and is superimposed over a spectrum of a useful signal that needs to be received by the receiving channel, namely, falls within a receiving band of the receiving channel, receiving performance of the channel will be affected.
A possible radio frequency receiver solution is to dispose multiple frequency synthesizers on different chips, which can relatively effectively solve a mutual-interference problem of multiple frequency synthesizers. However, when the multi-chip solution is applied, a price to be paid is that areas and costs increase sharply, which conflicts with increasingly intense requirements, at present, of a mobile terminal on a small size and cost efficiency of a radio frequency subsystem.